Planets and Exoplanets In The Universe

Hi Everyone! This is Ramesh here and today
we will know about this most familiar space object known as a Planet. A planet is an astronomical object that is
massive enough to get spherical shape due to its own gravity, not so hot and dense to
start nuclear fusion process and its surrounding region should be free of planetesimals or
smaller bodies. The planet word came from the Greek word planētai
which means wanderer. Planets are divided into two main categories:
smaller Rocky terrestrials and low-density Giant planets which are further divided into
Gas giants and ice giants. In the solar system, there are 8 planets:
Out of which Mercury, Venus, Earth, and Mars are rocky planets whereas Jupiter, Saturn,
Uranus, and Neptune are low-density Giant planets. Jupiter and Saturn are Gas Giants mainly composed
of Hydrogen and helium. On the other hand, Uranus and Neptune are Ice Giants composed
of water, methane, and ammonia having a thick atmosphere of hydrogen and helium. In 2006, a new category of Planet was adopted
by the International Astronomical Union called Dwarf planets. Like planet a dwarf planet
orbit a star and is massive to form a spheroid shape, but is not capable to clear its surroundings
from other smaller bodies. Pluto has been demoted from planet to dwarf
planet because it is unable to dominate its neighborhood as a planet does. This demotion
of pluto has been highly criticized. Right now, only 5 Solar system objects are
recognized as dwarf planets: Pluto, Eris, Ceres, Haumea, and Makemake. Except for Ceres,
all are found beyond the region of Neptune called Kuiper belt. In the following animation, we will look into
the size, gravity, and distance of planets and dwarf planets from the sun. Let’s get
right into it… No one knows with certainty how planets are
formed. A prevailing theory proposes that planets are formed from the leftover gas and
dust materials in the process of star formation. When dust and gas collapse a protostar is
formed at the core, surrounded by a rotating protoplanetary disk. By the accretion process,
dust particles in the disk continuously and gradually gather mass to form larger objects
or known as planetesimals. When planetesimals forms, the accretion process
speeds up because it attracts nearby material by its own gravity. As objects become more
and more massive it collapses inward under its own gravity to form protoplanets. Protoplanets are minor planets that are even
smaller than the dwarf planets. Some protoplanets continue to collide with other planetesimals
or another protoplanet until they are massive enough to become a planet. Depending upon the past matter solid or gas
used in accretion, the fate of a planet is decided whether it will be a rocky terrestrial
or a gas giant or an ice giant. In 1992, radio astronomers Aleksander Wolszczan
and Dale Frail discovered two planets orbiting a pulsar PSR 1257+12. This discovery is considered
to be the first precise detection of planets outside the solar system. These planets are
termed as Exoplanets or extrasolar planets. On October the 6th 1995 the first exoplanet
orbiting a main-sequence star 51 Pegasi was discovered by Michel Mayor and Didier Queloz
of the University of Geneva. After that thousands of exoplanets including terrestrial and gas
giants have been discovered. Exoplanets like Super-Earth, Mini-Neptune,
and Hot Jupiter have not been found yet in our solar system.
Giant Planets that orbit too close to the sun are called hot Jupiters. They resemble
planet Jupiter but revolves its parent star in less than 10 days. Its orbit is even less
than one-tenth of the Earth orbit. One of the best known hot Jupiter is 51 pegasi
b. Exoplanets that revolve around the galactic
center directly instead of a Star are known as Rogue Planets. The reason is either they
are ejected from the planetary system or never been gravitationally bound by any star or
its remnant. In the upcoming animation, we will look into
the size of planets and exoplanets found in our universe and its distance from earth in
light-years. Our moon is 384,400 km from earth. Have you
ever wonder, how our planets will look like if it comes, as close as our moon is to earth?
Let’s find out… Some Exoplanets are found to be potentially
habitable. These planets are at the right distance from its parent star for liquid surface
water to be present. This region of a star is called habitable or Goldilocks zone where
the temperature of the planet is not too cold or too hot. Let’s look into the size of potentially
habitable exoplanets and its surface temperature. I hope you learn something from this episode
on planets. Thank you for like, share, comment and subscribe. Hope you guys have a wonderful
day and I will see you next time. Thanks for watching!


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